In the image forming apparatus, a toner image is formed on the recording material (sheet), and the recording material, on which the image is formed, is heated and pressed, so that the image is fixed on the recording material.
In Japanese Laid-Open Patent Application No. 2006-163298 and Japanese Laid-Open Patent Application No. 2014-59549, a fixing device for heating the toner image on the recording material by nipping the recording material at a nip between an endless belt, which is an example of a rotatable heating member, and a pressing roller, which is an example of a rotatable pressing member, is disclosed. In this fixing device, a heater is contacted to an inner surface side of the belt, so that the belt is heated. This heater is provided with a temperature detecting element for detecting a temperature of the heater, and the fixing device carries out electrical power supply to the heater on the basis of output of the temperature detecting element.
Further, an image forming apparatus disclosed in Japanese Laid-Open Patent Application No. 2006-163298 improves a first print out time by executing an image forming process in parallel to a temperature raising process of the fixing device. Specifically, when the temperature detecting element detects that the heater warms up to a temperature to some degree, feeding of the recording material is started so that the recording material is fed to the fixing device at timing when a temperature of the fixing device has increased to a fixing temperature.
In Japanese Laid-Open Patent Application No. 2002-351254, a temperature detecting sensor, including a sponge and a thermistor, is disclosed. Such a temperature detecting sensor changes in responsiveness depending on use status in some cases, and, therefore, in Japanese Laid-Open Patent Application No. 2012-198271, correction of a detected temperature is carried out using two temperature detecting sensors.